For hearing impaired persons, the use of hearing aids can amplify ambient sounds to effectively help them hear the ambient sounds clearly. This is of great assistance to those hearing impaired persons in living and learning. However, although modern hearing aids are compact and are convenient to carry, hearing aids still cannot process sounds as precisely as the human ears, which can filter out annoying noise, such as wind noise caused by blowing wind. Generally speaking, when wind blows against the hearing aid, the hearing aid will amplify the sound of the wind as it is designed to, thereby producing a very loud noise. Such unexpected noise often causes much discomfort to the user. Therefore, three conventional techniques have been proposed to alleviate the problem of wind noise.
In U.S. Patent Application Publication No. US20040161120A1, entitled “Device and Method for Detecting Wind Noise,” there is disclosed a method to avoid the aforesaid problem. As disclosed in said patent publication, two input signals are transmitted to a low-pass filter, and computation results of a cross correlation function and an auto-correlation function of the filtered signals are compared to detect the presence of wind noise. However, since the method disclosed in the aforesaid publication is used to detect whether signals in a fixed low-frequency distribution are low-correlated, and is not only directed to wind noise, the effect is quite unsatisfactory. This is because there are many other noises belonging to such low-correlated signals in the fixed low-frequency distribution, e.g., non-voiced speech and ambient noise in a closed room.
In addition, in U.S. Pat. No. 6,741,714B2 “Hearing Aid with Adaptive Matching of Input Transducers,” there is disclosed a hearing aid device that includes a plurality of input transducers, where the input transducers have a directional characteristic under normal conditions. When one of the input transducers receives wind noise, all of the input transducers will be switched from the directional characteristic to an omni-directional characteristic so as to reduce the effect of wind noise. One of the ways to detect the presence of wind noise is to determine whether a plurality of input transducer signals at a given time point have the same sign and from that time on measure the occurrence number of these input transducer signals having opposite signs at each time point within a time interval. If the occurrence number is greater than a threshold value, a wind signal is determined. This method determines wind noise based on whether the plurality of input transducer signals have the same sign. However, since the characteristic of wind noise is not absolutely like this, the result is not accurate.
Furthermore, in U.S. Pat. No. 6,882,736B2 “Method for Operating a Hearing Aid or Hearing Aid System, and a Hearing Aid and Hearing Aid System,” another method for detecting wind noise is disclosed. The concept of said patent is to calculate the correlation of a plurality of input signals by subtracting one input signal from another input signal. The higher the correlation between the signals is, the smaller the average value of the results after subtraction will be. If the average value is greater than a threshold value, this indicates the presence of wind noise. Since said patent determines the correlation of the input signals merely with simple calculations, wind noise cannot be accurately detected.
All of the three above-mentioned prior art techniques fail to accurately detect wind noise and may mistake other types of noise for wind noise, thereby incurring incorrect processing. Therefore, there is a need for a solution.